Effect of ECG-gating Retinal Photographs on Retinal Vessel Caliber Measurements in Subjects with and without Type 2 Diabetes

ABSTRACT

Purpose/Aim of this study: Retinal vessel caliber is an independent risk marker of cardiovascular disease risk. However, variable mechanical delays in capturing retinal photographs and cardiac cycle-induced retinal vascular changes have been shown to reduce the accuracy of retinal vessel caliber measurements, but this has only ever been investigated in healthy subjects. This cross-sectional study is the first study to investigate this issue in type 2 diabetes. The aim of this study was to determine whether ECG-gating retinal photographs reduce the variability in retinal arteriolar and venular caliber measurements in controls and type 2 diabetes.

Materials and Methods: Fifteen controls and 15 patients with type 2 diabetes were arbitrarily recruited from Westmead Hospital, Sydney, Australia. A mydriatic fundoscope connected to our novel ECG synchronization unit captured 10 ECG-gated (at the QRS) and 10 ungated digital retinal photographs of the left eye in a randomized fashion, blinded to study participants. Two independent reviewers used an in-house semi-automated software to grade single cross-sectional vessel diameters across photographs, between 900 and 1800 microns from the optic disc edge. The coefficient of variation compared caliber variability between retinal arterioles and venules.

Results: Our ECG synchronization unit reported the smallest time delay (33.1 ± 48.4 ms) in image capture known in the literature. All 30 participants demonstrated a higher reduction in retinal arteriolar (ungated: 1.02, 95%CI 0.88–1.17% vs ECG-gated: 0.39, 95%CI 0.29–0.49%, p < .0001) than venular (ungated 0.62, 95%CI 0.53–0.73% vs ECG-gated: 0.26, 95%CI 0.19–0.35%, p < .0001) coefficient of variation by ECG-gating photographs. Intra-observer repeatability and inter-observer reproducibility analysis reported high interclass correlation coefficients ranging from 0.80 to 0.86 and 0.80 to 0.93 respectively.

Conclusion: ECG-gating photographs at the QRS are recommended for retinal vessel caliber analysis in controls and patients with type 2 diabetes as they refine measurements.

KEYWORDS:

• Electrocardiography
• pulsatile flow
• retinal vessels
• type 2 diabetes

Acknowledgments

This manuscript is a revised and updated version of Dr. Anchal Lal’s doctoral thesis.⁴⁰ The authors thank Dr. Kiran A. Jacob (Westmead Hospital, NSW, Australia) for her contribution to retinal vessel caliber analysis, and all the research participants for giving up their time and their cooperation throughout the study.

Declaration of interest statement

The authors have no financial or non-financial competing interests to report. The funding organisation had no role in the design and conduct of the study; collection, management, analysis and interpretation of the data; and preparation, review or approval of the manuscript; and decision to submit the manuscript for publication.

Contributors

AL, OG, MAB, PM and AT participated in the design and conception of the study. AL conducted the study and acquired the data. AL, ND and AS analyzed the data, performed statistical analysis and together with AT contributed to the data interpretation. AL, ND, MAB and AT wrote the paper. All authors participated in reviewing and revising the manuscript, and approved the final version. AL is responsible for the integrity of the work as a whole and serves as guarantor of this work.

Data availability statement

The raw quantitative dataset used to support the findings of this study is deidentified participant data and is available from the corresponding author on reasonable request. Please contact Dr Anchal Lal at [email protected] if interested.

Additional information

Funding

This project was funded by the Diabetes Australia Research Trust [general grant reference number Y11-MITP].